It took quite a bit more convincing before Knox finally left the library.
As soon as he closed the door behind him, Cozy took off to grab the tome she'd sought after. The book that could tell her how to get her object back for Zecora's spell. The book that could tell her how to safely open the gates.
Her flight was thrown slightly askew by the pain emanating from her leg, but she still made it to where the book still sat on the shelf. She'd have to improvise a new plan to get it out of the school. After all, she couldn't very well walk out with school property if Knox was around.
She quickly scanned her surroundings, finding a backpack under one of the nearby tables.
'Perfect,' she thought. 'One of the students must've left it here.'
It was exactly what she needed. Now, she could grab the book and hide it out in the school courtyard until she can come back to get it. The backpack would keep it safe from the elements until then, and she could just put the backpack in the lost and found bin after she was done with it.
She opened the backpack and gently slid the tome inside. Of course, true to form, that's when bad luck chose to strike. An aura of pale pink magic wrapped itself around the doorknob yet again, and Knox casually walked into the room.
"Just thought I'd make sure you weren't hungry or anything," he said. "I forgot to ask earlier."
"No, I'm good," said Cozy nervously, the backpack still lying in plain sight right next to her.
Knox drifted his gaze from her to the backpack.
"Where'd you get that?" he asked.
"Oh, I just... found it over there!" she said, gesturing towards a random part of the library.
"Well, I'll take it to the lost and found for you," he said.
"No, I'll take it," she said.
"Ummm... Your leg," he said, as if Cozy was supposed to know exactly what he meant.
She did.
It was true. Her injured leg should probably be used as little as possible. However, this didn't deter her.
"Ummm... My wings," she rebutted. "I'll just fly it there while you finish your work for the night."
Knox muttered something under his breath as he opened the door, holding it open for Cozy to follow him out.
Once they were both in the hall, they split up and went in opposite directions down the corridor. Both of them turned corners at their respective ends of the hall. A few moments later, however, Cozy came flying lopsidedly back towards the library door.
She opened the door carefully, so as not to make enough noise to attract Knox's attention. She made her way towards the window Ocellus had left open, but her lopsided flying finally got the best of her. Her shoulder collided with a bookshelf less than ten feet away from the window, knocking one of the larger books off of a higher shelf.
This wouldn't have been much of a problem... if the falling book hadn't directly hit Cozy's injured forehoof. She cried out as pain shot through her leg with the impact.
The pain was blinding, and forced her to fall to the floor. Nonetheless, she knew she had to act fast. Knox was sure to have heard her scream, and he'd be there any moment. As pink magic enveloped the entire door and it came flying open, Cozy managed to throw the backpack out the open window.
After that, Knox made her come home with him. She didn't even argue this time. The book was safely outside, and the pain in her leg had now become more than she could bear.
The next day, after a quick checkup for her leg with Nurse Redheart, Cozy flew back to the school courtyard. She immediately went to the space directly outside the library window.
She gasped, and her heart began racing as she slipped into yet another panic attack.
The backpack, and more importantly the book inside, was gone.
Interesting. My guess is that Discord stole the book.
I kind of figured that Ocellus, if she is still as skeptical as she had been before, may be lingering around to see if Cozy is up to no good. If it is Ocellus, she's probably already with the remainder of 'The Student Six' and reviewing the book in the backpack. Moreover, if this is the scenario, Ocellus is the most scholarly of the group and would be eager to scrutinize the connection between the book and why cozy wanted it.
Now we have some serious suspense. Was it Ocellus who took the book? How will Knox react if he is brought to discuss cozy's late-night activities. There really isn't anything to stop Ocellus from going to Starlight and sunburst. Starlight could then easily get to twilight and, well, the chaos would be worth Discord's time for sure.
This also leaves open how Discord could have taken the book. He may be looking it over and delighting in all the ways he can 'play' with cozy Glow having something to hold over her.